To provide an optical transmission module for receiving the light of a VCSEL by a light receiving element for an optical output monitor, which has no variation in quality and has excellent manufacturability.

The optical transmission module 1 is provided with electronic elements such as the VCSEL 2 and a PD 3 inside a package, sends out the light from the main light emitting surface of the VCSEL 2 to an optical fiber, and receives the light from the back surface of the main light emitting surface by the PD 3 for the optical output monitor. In the optical transmission module 1 the package is configured by attaching a lid 5 with planar glass 5c to a laminated substrate 4 where a recessed part 4a for mounting the electronic element is formed in a lamination direction so as to cover the recessed part 4a, and the recessed part 4a of the laminated substrate 4 has a step part 4c having a level difference in the lamination direction relative to the bottom surface 4b of the recessed part 4a. The PD 3 is mounted on the bottom surface 4b of the recessed part 4a, and the VCSEL 2 is mounted on the upper surface of the step part 4c so that the light from the back surface is received by the PD 3.